The present invention relates to a file storage service system, comprising a path denotative NAS server and an ID denotative NAS server. In particular, it relates to a technique to allow a file in the path denotative NAS server to migrate into the ID denotative NAS server, and a technique to access a file in the path denotative NAS server from an ID denotative NAS client.
An NAS (Network Attached Storage) system is known as a file storage service system of a client/server type. In the NAS system, when an NAS server receives an access request from an NAS client via a network such as WAN and LAN, the NAS server performs a process according to the requested contents (write/read). In other words, when the NAS server receives from the NAS client a write request with a file the NAS server writes the file into a disk device of its own server and retains the file. When the NAS server receives from the NAS client a read request with a denotation of file, the NAS server reads out the denoted file from the disk device of its own server, and sends the file to the NAS client.
In the meantime, in the aforementioned NAS server, a denotation of a file received from the NAS client is performed based on a deposit location of the file. The deposit location of the file comprises a node name and a file path name, such as “hitachi.co.jp/usr/home/foobar/doc/memo.txt”. Here, “hitachi.co.jp” corresponds to the node name, and “/usr/home/foobar/doc/memo.txt” corresponds to the file path name. Hereinafter, in the present specification the NAS server and the NAS client of a type in which the file denotation is performed based on the file deposit location will be referred to as a path denotative NAS server and a path denotative NAS client. As the path denotative NAS server, there are an NFS (Network File System) server, a CIFS (Common Internet File System) server, or the like. Furthermore, there are documents of prior art describing the path denotative NAS server, “UNIX Internals: The New Frontiers”, authored by Uresh Vahalia, translated by Hideyuki Tokuda, Akira Nakamura, Yoshito Tobe, and Yoshiyuki Tsuda, issued by PEARSON Education, May 2000”, and “NFS illustrated” authored by Brent Callaghan, translated by QUIPU Corporation, issued by ASCII Corporation, Sep. 20, 2001
Recently, a file storage service system, celled as a distributed parallel NAS system, has been suggested. In the distributed parallel NAS system, a file is divided into fragments and they are stored in a plurality of NAS servers in a distributed manner. Therefore, it has been found difficult for the NAS client to perform the file denotation based on the file deposit location, since it is necessary for the NAS client side to grasp all the deposit locations for every fragment. Then, in many of the distributed parallel NAS systems, the NAS server handles the file denotation received from the NAS client, based on a file identifier called as GUID (Global Unique Identifier). When the NAS server receives a write request with a file from the NAS client, the NAS server divides the file into a plurality of fragments, and stores the fragments in a plurality of NAS servers including its own server in a distributed manner. In addition, the NAS server generates a GUID of the file, notifies the NAS client of the GUID thus generated, and manages each of the deposit locations of the fragments in association with the GUID. When the NAS server receives from the NAS client a read request with a denotation of the QUID, the NAS server specifies a plurality of deposit locations being associated with the denoted GUID, restores the file by reading out the fragments respectively from the specified deposit locations, and sends the restored file to the NAS client. As the GUID, for example, a hash value of the file contents is used. The GUID and a method for converting the GUID into file deposit locations are described in “Distributed Content Location for Ubiquitous Environments” authored by Kiyohide Nakauchi, Hiroyuki Morikawa, and Tomonori Aoyama, Technical Report of the Institute of Electronics, Information and Communication Engineers, NS2002-110 IN2002 CS2002, September 2002.
Hereinafter in the present specification, an NAS server and an NAS client of a type in which a file denotation is performed based on the GUID, will be referred to as ID denotative NAS server and ID denotative NAS client. As the ID denotative NAS server, there are “The OceanStore Project” operated by University of California Berkeley Computer Science Division in the U.S. and “PASIS” operated by Carnegie Mellon University in the U.S. As documents of prior art by “The OceanStore Project”, there are “The OceanStore Project Providing Global-Scale Persistent Data”, UC Berkeley Computer Science Division [online] (retrieved on Mar. 1, 2003), Internet <URL: http://oceanstore.cs.berkeley.edu/>, a “Maintenance-Free Global Data Storage” appears in IEEE Internet Computing Vol. 5, No 5 September/October 2001, pp, 40-49, authored by Sean Rhea, Chris Wells, Patrick Eaton Dennis Geels, Ben Zhao, Hakim Weatherspoon, and John Kubiatowicz. As documents of prior art by “PASIS”, there are “PASTS Engineering Survivable Storage”, Carnegie Mellon University [online] [retrieved Mar. 1, 2003] Internet <URL: http://www.pdl.cmu.edu/Pasis/index.html>, and “Survivable information storage systems” IEEE Computer 33(8):61-69, August 2000, authored by Jay J. Wylie, Michael W. Bigrigg, John D. Strunk, Gregory R. Ganger, Han Kiliccote, and Pradeep K. Khosla.